With the wide application of nano-technologies, methods for preparing nanofibers via electrospinning are getting more and more attentions in experimental study and industrialized development. Due to its moderate preparation process and nano-level fiber fineness, solution electrospinning attracts deep study and wide application, and batch production is preliminarily realized at present. However, due to the use of solvents, the industrialization continuity, the production environment and the application in medical areas are limited; and because problems of noxious solvent recovery, low strength of porous fiber, being difficult to prepare PP and PE fiber and low efficiency, etc., exist in solution electrospinning, the industrialized application of solution electrospinning technologies is limited. No solvent is used in melt electrospinning, so it has an intrinsic safety, and the fiber prepared by melt electrospinning may reach several hundreds of nanometer, which is one order of magnitude less than the fineness of fiber prepared by the traditional melt blowing technology. Therefore, melt electrospinning may be regarded as a reliable technology for realizing the environment-friendly production of high-performance nanofibers.
In 1981, Larrondo and Manley reported a electrospinning of polymer melt for the first time, and they designed a melt electrospinning device in which the melt is extruded via a piston and the collection distance for the electrospun fiber is 3 cm. When electrospinning PP by this device, fibers with a diameter of about 50 μm can be prepared successfully.
Naoki SHIMADA, et al. from Japan prepares a row of fibers by heating a membrane to a very low viscosity via a customized line laser light source, thus the output of fibers is increased based on the original point light source, but the cost is still very high, and the output is low, thereby it is difficult to realize batch production.
Michal KOMAREK and Lenka MARTINOVA from Czech Republic University, Czech Republic proposed a slit-type spinning device, but such a spinning device cannot well solve the uniform distribution of melt at the slit, and the number of threads is not enough for industrialized application.
US Patent US20090121379A1 proposed electrically-assisted melt blowing and hot air-assisted electrospinning, wherein the high-speed stretching effect of hot air and the unstable refining effect of electric field force are combined, and the jet flow speed of the single thread is increased under the action of hot air blowing, and the fiber fineness is made to reach about 200 nm under the action of the electric field force; however, the nozzle used in this patent is a single nozzle for single jet generation and its improvement, and the embodiments are only directed to solution spinning, moreover, only methods are put forward for melt spinning, which is limitative for industrialized application.
Yao Yongyi et al., from Sichuan University mentions an air flow-electrospinning machine in document “Electrospinning Method And Air Flow-Electrospinning Method For Preparing Polysulfone Nanofibers”, wherein, an air passage system is wrapped outside an ordinary single-needle nozzle, and the jet flow is stretched by a resultant force of the electrostatic force and the friction force between the air flow and the polymer jet flow, thereby the fibers spun are refined, however, the structure of the nozzle is complex, which is adverse to industrialized application, and moreover, a set of air supply device needs to be added additionally, thus the cost will be added, and the energy consumption will be large.
Xia Lingtao et al. from Beijing University of Chemical Technology mentions the modification of polypropylene by a super-branched polymer in document “Application Of Super-Branched Polymer In Melt Electrospinning”, thereby the viscosity of polypropylene melt may be lowered, and the fiber spun will be finer.
At present, the key problem to be solved for melt electrospinning is how to further decrease the micrometer-level fiber diameter to hundred nanometer-level (submicrometer-level) fiber diameter and how to further increase the production efficiency of melt electrospinning for industrialization.
Therefore, the diameter of fibers produced by the existing melt electrospinning device is large, and it is difficult for industrialized application.